Ebook Handbook of clinical anaesthesia (4/E): Part 2

14

Neurosurgery
ELEANOR CHAPMAN

Anaesthesia for intracranial
neurovascular surgery
353
References356
Anaesthesia for magnetic resonance
(MR) imaging
356
References359
Anaesthesia for non-craniotomy
neurosurgery359

ANAESTHESIA FOR INTRACRANIAL
NEUROVASCULAR SURGERY
Patients may require neurosurgery for treatment of
cerebral aneurysms, arteriovenous malformations
and other vascular abnormalities, or following intracranial haemorrhage.

CEREBRAL ANEURYSMS
Most patients present acutely following aneurysm
rupture with the signs and symptoms of subarachnoid haemorrhage (SAH). Unruptured aneurysms
are increasingly being detected incidentally on cranial radiological investigations but can also present
with symptoms related to mass effect.

NEUROSURGICAL TREATMENT
Endovascular techniques (coiling) have been
shown to be preferable to an open approach (clipping) for patients with ruptured aneurysms. Open

References362
Anaesthesia for posterior fossa surgery 362
References365
Anaesthesia for spine surgery
366
References368
Anaesthesia for supratentorial surgery 369
References373

neurosurgical clipping has thus become increasingly
uncommon unless the aneurysm
• Has a wide neck or difficult anatomy
• Is too distal to reach endovascularly
Although mortality and disability have been
shown to be reduced at 1 year, long-term coiled
aneurysms are 8 times more likely to rebleed.
Consideration should be taken in the under 40s to opt
for open neurosurgical clipping. The optimum timing for securing a ruptured aneurysm is still unclear,
with little evidence that performing surgery within
24 hours confers any benefit over 24–72 hours.

PREOPERATIVE ASSESSMENT
• Patients with poor grade SAH may already be
intubated and ventilated on ICU.
• If conscious, a neurological exam needs to
document the GCS, cranial nerve involvement
and any sensory or motor deficit.
• Patients should have their headache controlled
with appropriate analgesia.

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Neurosurgery

• Continue nimodipine and anticonvulsants
where necessary.
• Optimise cardiac function; a preop ECG is
mandatory.
• Extremes of blood pressure should be avoided;
keep MAP <110 mmHg and SBP <160 mmHg
while ensuring a CPP of 60 mmHg.

INTRAOPERATIVE MANAGEMENT
Anaesthetic management is similar to that of any
neurosurgical procedure involving raised ICP but
particular attention should be paid to:

354

• Careful induction avoiding surges in blood
pressure where an increase in transmural
pressure in the affected artery could precipitate
a further rupture. Conversely, hypotension may
worsen ischaemia and cause infarction.
• In addition to standard monitoring, invasive
blood pressure monitoring is essential.
Frequently central venous access is inserted
if the patient is likely to need hypertensive
therapy postoperatively. Temperature

monitoring is advisable as is a urinary catheter
as a lot of contrast and flushes will be used in
coilings.
• Propofol TIVA, sevoflurane or desflurane
accompanied by remifentanil to keep the MAC
<1.0 are appropriate choices for maintenance.
• Maintain normocarbia, normoglycaemia and
normothermia.
• Cardiac dysfunction and arrhythmias are
common and should be managed with
correction of electrolyte imbalances in the first
instance.
• Position supine for all coiling procedures and
anterior circulatory aneurysm clipping but for
posterior aneurysms the patient will need to be
in the park bench or prone position.
• During clipping the surgeon might use a
temporary clip while dissecting around
the aneurysm to reduce the risk of further
rupture. Whilst these clips are in place the
surgeon may ask for some cerebral protection
in the form of mannitol 20% as a free radical
scavenger, metabolic suppression with a bolus
of thiopental or hypothermia.

INTRAOPERATIVE ANEURYSM
RUPTURE
Intraoperative aneurysm rupture occurs most commonly as the neck is dissected. At this stage, a temporary clip can be used to stop haemorrhage from
the main vessel. However, if the aneurysm ruptures
as the dura is being opened, and the circle of Willis is

not dissected, the situation will be uncontrolled. Under
these circumstances, acute hypotension is essential
to allow surgical access and control of haemorrhage.
Blood pressure should be reduced only to a level that
allows the surgeon to gain control under direct vision.
If a rupture is suspected while undergoing coiling, the goals are to both lower the blood pressure
and to increase the coagulation by reversing any
heparin. Techniques may be required to lower ICP.
Once the bleeding is controlled, the blood pressure
should be raised again to check for leaks and then
proceed again with coiling.

CEREBRAL OCCLUSION
AND VASOSPASM
During coiling, ischaemia may be noticed intra­
operatively. This may be due to thromboembolism,
arterial dissection, catheters, coil misplacement
or vasospasm. Management should be to increase
blood pressure to improve the contralateral flow. The
radiologists may ask for IV antiplatelet therapy, heparin or thrombolytic therapy or may give nimodipine
direct to the vasospasm themselves.

POSTOPERATIVE MANAGEMENT
• Grade I, II and most III SAHs with uneventful
intraoperative course should be extubated using
a technique to avoid coughing and surges in
blood pressure (e.g. remifentanil with 5–10 mg
boluses of labetalol where appropriate).
• It is prudent to send all patients to ICU as many
will develop further complications such as

delayed cerebral ischaemia or non-neurological
complication.
• Grade IV and V patients should be transferred
back to ICU with continued ICP monitoring
and a sedation hold or trial of extubation taken
in a timely manner.


Anaesthesia for intracranial neurovascular surgery

ELECTIVE ANEURYSMS
Elective aneurysms are less unstable preoperatively
but the procedures are essentially the same. The
complications (vasospasm, rebleeding) are much less
likely and following coiling, patients can usually be
extubated and discharged to level one care.

ARTERIOVENOUS MALFORMATIONS
Arteriovenous malformations (AVMs) are congenital abnormalities of the vascular network in which
abnormal connections between arteries and veins,
without intervening capillary, result in a direct arterial-​
to-venous shunt and development of twisted dilated
vessels. Approximately 5%–10% of AVMs present
acutely following an SAH, but the majority present
with seizures, headache or progressive neurological
signs.
Many AVMs are now treated by staged radiological glue embolization and/or gamma knife. For
85%–95% this may be curative but, in others, surgical
excision is required.
• Anaesthesia is very similar to that of aneurysm

surgery.
• If open surgery is undertaken, there is great
potential for bleeding and cross-matched blood
should be available.
• Postoperatively sudden restoration of a
chronically hypotensive area of brain can
overwhelm the autoregulatory mechanisms
resulting in microhaemorrhage and diffuse
swelling: normal perfusion pressure
breakthrough syndrome.
• Surges in blood pressure during extubation
can be particularly problematic so an
antihypertensive agent (labetalol 5–10 mg
boluses) should be ready to use.
• In the postoperative period, blood pressure
should be kept low-normal with labetalol or
esmolol infusions where necessary.

INTRACRANIAL HAEMORRHAGE
Intracranial haemorhage (ICH) is a devastating
cause of stroke. It consists of 10%–15% of all strokes
and 85% of all intracerebral haemorrhages. The

30-day mortality is 40%–50% and of the survivors
only 20%–25% are able to function independently
at 6 months. The aetiologies for ICH are detailed in
Box 14.1. Most patients present with a rapid onset
neurological deficit associated with vomiting, headache, seizures and decreased level of consciousness,
including coma.
Patients may need surgical intervention for:

• Evacuation of clot (particularly in peripheral
clots and cerebellar haematomas)
• Insertion of EVD (for hydrocephalus due to
ventricular extension)
• Decompressive craniectomy
• Insertion of catheter for thrombolysis (currently
under trials)
Specific issues related to the management of ICH:
• Anaesthetic considerations are similar to
other neurovascular procedures. Many
patients will already be intubated and
ventilated on ICU.
• Patients often have cardiac and other
systemic complications related to the acute
haemorrhage and also chronic hypertension;
as such, invasive blood pressure monitoring is
mandatory.
• While it is important to avoid extremely
high blood pressure to avoid haematoma
expansion, strict lowering of systolic blood
pressure to 110–140 mmHg has failed to show
benefit.
• Postoperative ICU care is often required and
an ICP monitor should be inserted at the end of
surgery if the patient will remain sedated.

BOX 14.1: Risk factors of primary
intracranial haemorrhage
▪▪
▪▪

▪▪
▪▪
▪▪
▪▪
▪▪
▪▪

Increasing age
Male sex
African/Asian descent
Chronic hypertension
Amyloid angiopathy
Anticoagulation treatment
Excess alcohol
Recreational drugs, e.g. cocaine, ecstasy

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Neurosurgery

REFERENCES
Doriraj IL, Hancock SM. (2008). Anaesthesia for
interventional neuroradiology. Contin Educ
Anaesth Crit Care Pain 8: 86–89.
Fogarty Mack P. (2014). Intracranial haemorrhage:
Therapeutic interventions and aneasthetic management. Br J Anaesth 113: 17–25.
Hartmann A, Mast H, Choi J et al. (2007). Treatment
of arteriovenous malformations of the brain.
Curr Neurol Neurosci Rep 7: 28–34.

Kundra S, Mahendru V, Gupta V, Kumar
Choudhary A. (2014). Principals of neuroanaesthesia in aneurysmal subarachnoid
haemorrhage. J Anaesthesiol Clin Pharmacol 30:
328–337.
Molyneux A, Kerr R, Stratton I et al. (2002).
International Subarachnoid Aneurysm Trial
(ISAT) of neurosurgical clipping versus endovascular coiling in patients with intracranial
aneurysms. Lancet 360: 1262–1263.

CROSS-REFERENCE
Subarachnoid haemorrhage, Chapter 3

ANAESTHESIA FOR MAGNETIC
RESONANCE (MR) IMAGING
Images are produced by placing patients within a
strong magnetic field and applying pulses of radiofrequency (RF) energy. This results in intermittent
release of RF energy from hydrogen nuclei, which is
detected by a series of close-fitting receiving antennae (coils). The RF signals are collected and interpreted by computer to produce extremely accurate
images. The strength of the magnetic field used is
measured in tesla (T). One tesla is equal to 10,000
gauss (G); the Earth’s magnetic field is approximately
0.5–1.5 G. The most common MR scanners in clinical use range from 0.5 to 3 T, although the majority is
1.5 T. The patient is placed in the centre of a magnetic
field within the bore of a magnet and, as a result, is
enclosed within a narrow tube to which access is
extremely limited. Newer designs include open and
356

wider bore magnets that allow improved access and
are less claustrophobic for awake patients.

MR scans are produced in sequences of up to
10 minutes and any movement during that time produces profound distortion of the final images. The
aim of anaesthesia for MR is therefore to provide
immobility while maintaining safety and patient
comfort throughout.

SAFETY ISSUES IN MR UNITS
• The strong magnetic field poses the most
important hazard related to anaesthesia and
care of patients requiring MR.
• Ferromagnetic objects within the 50 G line will
move and may be rapidly accelerated into the
magnetic field becoming dangerous projectiles
causing injury to anyone in their path, damage
to equipment and interference with the MR
image.
• Implanted ferromagnetic objects may move
in the magnet or heat up, causing local
tissue damage. This includes foreign bodies
in the eye that may be dislodged during
scanning, with the associated risk of vitreous
haemorrhage.
• Non-ferromagnetic metals may heat up
causing burns. They will also cause image
artefact if they are adjacent to the area being
scanned.
• Implanted pacemakers, defibrillators and other
devices may be inactivated, reprogrammed,
dislodged or revert to an asynchronous mode.
Although implanted programmed devices are

a general contraindication to MR, some may be
scanned under strictly controlled conditions in
specialist centres.
• Pregnant patients and staff should not enter the
scanner during the first trimester.
• No patients or staff should be allowed past the
5 G contour line without going through a check
for implantable devices or contraindications.
• Noise levels above 85 decibels may be
generated by the scanner and can cause
potential hearing loss in those having long
scans. Staff and all patients should wear ear
protection.


Anaesthesia for magnetic resonance (MR) imaging

The most commonly used intravenous MR contrast agent is gadolinium dimeglumine (Gd-DTPA),
which can cause nausea, vomiting and pain on
injection. It has an extremely low incidence of anaphylactoid reactions. However, Gd-DTPA has been
implicated in nephrogenic systemic fibrosis in
patients with impaired renal function. An assessment of renal function should be performed if a
patient’s scan requires contrast.

•
•

•

PRACTICAL CONSIDERATIONS

• The MR unit is often isolated so must be
self-sufficient in terms of anaesthesia and
resuscitation equipment.
• The patient is placed inside a narrow bore tube,
is relatively inaccessible and may be difficult to
observe. Many MR units were not designed with
anaesthesia in mind and space is often limited.
• Anaesthetic and recovery rooms should be
placed adjacent to the scanner.
• Ferromagnetic items such as scissors, oxygen
cylinders and laryngoscopes must never be
taken into the scanning room.

MONITORING AND EQUIPMENT
Monitoring should conform to the same standards as
anaesthesia or sedation in the operating theatre and
allow the anaesthetist to view monitor and patient
from outside the scanning room. Equipment is
• MR safe – No additional risks anywhere in the
MR environment.
• MR conditional – Pose no known hazard in the
MR environment with specified conditions of
use. Field conditions that define the specified
MR environment include field strength, spatial
gradient, rate of change of magnetic field, RF
fields and specific absorption rate.
• MR unsafe – Pose hazards in all MR
environments but necessary to have in adjacent
anaesthetic and recovery areas.
Additional considerations include:

• ECG cables must be shielded and special
electrodes used. Furthermore, the magnetic
field causes specific problems with ECG

•

interpretation, including MR-induced changes
in the ST segment and T waves similar to those
seen with hyperkalaemia or pericarditis.
Pulse oximeters must use fibre-optic cables or
be telemetric to avoid burns.
There may be a delay in obtaining a
capnograph signal and monitoring of airway
pressures and gases because the sampling
tubing will be longer than normal.
Measurement of temperature is difficult but
the technology is now available to measure
peripheral temperature.
An anaesthetic machine with piped gases should
always be available inside the scanning room
and this should be MR conditional. Non-MR
conditional anaesthetic machines must either
be bolted onto the floor or kept outside the 50 G
line. All gas cylinders must be MR safe.

PATIENT ASSESSMENT
Patients who may require general anaesthesia during MR scanning are shown in Box 14.2. Screening
is essential to exclude those who cannot enter the
magnetic field, and this is conducted using a standard
checklist. The exact make of an implantable device is

required in order to assess its safety in the MR scanner.
All patients with traditional pacemakers and internal
defibrillators may be excluded, as these devices may
be inactivated by the magnetic field. Any metallic
implants must be screened because aneurysm clips,
cochlear implants and prosthetic heart valves may
become dislodged, heat up or cause the induction of

BOX 14.2: Indications for general
anaesthesia during MRI
▪▪
▪▪
▪▪
▪▪
▪▪
▪▪
▪▪

Children
Ventilated and other ICU patients
Patients with severe movement disorders
Patients whose position is limited by pain
Adults with learning disorders
Claustrophobic patients
Certain patients undergoing stereotactic
neurosurgical procedures
▪▪ Patients receiving intraoperative MR

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Neurosurgery

electric currents. Patients who are metal workers or
who have known intraocular foreign bodies must be
screened with a plain X-ray prior to scanning and all
female patients should have a pregnancy test.
Tattoos may heat up in the magnetic field.
The increasing use of MR scans and pacemakers
has prompted manufacturers to develop MR conditional pacemakers. These have less ferromagnetic
components and behave more predictably with a
dedicated ‘MRI mode’ that needs to be switched on
before entering the scanner and switched off immediately afterwards. They are not, however, MR safe
and specific conditions of the pacemaker, the leads
and the scanner need to be met before you can proceed with a scan.

ANAESTHETIC MANAGEMENT
An MR scan is not painful, and the requirements
are therefore hypnosis, amnesia and immobility.
Recovery will be rapid and most patients can be
treated as day cases. The following rules facilitate
anaesthesia in the MRI suite:
• The patient is anaesthetized on a tipping trolley
in the anaesthetic room.
• Use short-acting agents and a laryngeal
mask (LM). With a standard LM, the pilot
balloon must be taped away from the site to
be scanned, as the small spring inside may
cause artefact. The airway should be clear as
partial airway obstruction may cause increased

respiratory movement and image artefact.
• Maintenance is usually easier with an
inhalational agent as this avoids the need for
MR compatible infusion pumps or the use of
long extensions and a pump placed outside the
50 G line.
• Patients with a poor gag reflex or oesophageal
reflux and pregnant women may need
intubation and ventilation. A preformed
endotracheal tube will allow close-fitting head
coils to be applied, but the pilot balloon must
again be taped away from the site to be scanned.
• Padding should be placed between the patient’s
skin and monitoring cables to prevent burns.
Loops in cables must be avoided.
358

• Patients are transferred to a docking table or
are taken into the scanning room on a nonferromagnetic trolley.
• Contrast may be needed for scans to examine
tumours or for MR angiography.
• In the event of a cardiac arrest or other critical
incident, the patient must be removed from the
scanner for resuscitation.

SEDATION
Many patients can have MR successfully performed
under sedation.

ADULTS

• Claustrophobic adults may often be adequately
managed with oral benzodiazepines.
• Pulse oximetry should be used in all cases.
• Short MR sequences may improve compliance.
• Intravenous sedation must always be given
by an anaesthetist and with extreme caution.
Monitoring of ETCO2 is advisable.
• Bolus doses of midazolam or low-dose
propofol/remifentanil infusion are frequently
used.

CHILDREN
• Young children cannot lie still without being
asleep and conscious sedation may not ensure
compliance because of the noise in the scanner.
• Small infants will sleep deeply after a feed.
• Children over 7 years are often compliant
without sedation.
• Many anaesthetists recommend general
anaesthesia, rather than sedation, for children
under the age of 7 years.
• Sedation must always be performed by
adequately trained personnel and with extreme
care. In some busy paediatric MR units, nurseled sedation techniques have been developed.
• Sedation techniques include chloral hydrate,
benzodiazepines and low-dose propofol
infusion.
• Supplemental oxygen should always be given
and adequate monitoring established.

Anaesthesia for non-craniotomy neurosurgery

INTRAOPERATIVE MRI
Intraoperative MRI (iMRI) during neurosurgical
procedures offers near real-time imaging surgical guidance. Intraoperative scanning allows the
surgeon to scan the patient at an appropriate time
during surgery and then conclude the surgical procedure or perform further resection. This approach
is associated with improved clinical outcomes and,
if repeated operations can be avoided, economic
savings.
The successful use of iMRI has been reported in
tumour surgery (ventricular tumours, gliomas, particularly low-grade and difficult pituitary tumours),
epilepsy surgery (including placement of depth electrodes for monitoring) and deep brain stimulation
surgery.
The concerns for safety, physiological monitoring
and equipment are the same as in the conventional
MRI environment but there is now the additional
focus on complex anaesthesia techniques, prolonged surgical procedures, repeated intraoperative scans, intraoperative thermoregulation and the
need for meticulous attention to patient positioning
on the operating table and during the transfer into
the scanner. With some procedures lasting more
than 6 hours, cases of hyperthermia have been
reported, possibly due to the RF heating effect of
the scanner.
The presence of a large multidisciplinary team in
the iMRI suite highlights the need for a compulsory
safety induction and training, and defined patterns
of workflow. During the surgery, an MRI responsible person, usually a senior radiographer, controls the flow of people and equipment through the
environment.

REFERENCES
Association of Anaesthetists of Great Britain
and Ireland. (2002). Provision of Anaesthetic
Services in Magnetic Resonance Units. London:
AAGBI.
Barua E, Johnston J, Fuji J et al. (2009). Anaesthesia
for brain tumour resection using intraoperative
magnetic resonance imaging (iMRI) with the

Polestar N-20 system: Experience and challenges. J Clin Anaesth 21: 371–376.
Ferreira AM, Costa F, Tralhao A, Marques H,
Cardim N, Adragao P. (2014). MRI-conditional
pacemakers: Current perspectives. Med Devices
(Auckl) 7: 115–124.
Lipson A, Gargolla P, Black P. (2001). Intraoperative
magnetic resonance imaging: Considerations for
the operating room of the future. J Clin Neurosci
8: 305–310.
Medicines and Healthcare Products Regulatory Agency.
(2007). Safety guidelines for m
­ agnetic resonance
imaging equipment in clinical use. MHRA Devices
Bulletin. London: MHRA.
Reddy U, White M, Wilson S. (2012). Anaesthesia
for magnetic resonance imaging. Contin Educ
Anaesth Crit Care Pain 12: 140–144.

CROSS-REFERENCES
Complications of position, Chapter 30

Day case surgery, Chapter 25

ANAESTHESIA FOR NONCRANIOTOMY NEUROSURGERY
STEREOTACTIC SURGERY
Stereotatic neurosurgery is used to facilitate precise
localisation of intracranial lesions. CT, MRI or digital
angiography is used to image the brain and provide
a three-dimensional reference to accurately define
the lesion. The initial step is to apply the extracranial
stereotactic frame which attaches to the head under
GA or a scalp block and sedation; this then acts as
the reference point for localisation. This method is
still utilised for the insertion of deep brain stimulators (DBS) for movement disorders and Parkinson’s,
epilepsy and when treating deep brain lesions closely
associated with important functional centres. More
recently frameless technology has developed using
small adhesive reference markers (fiducials) that are
attached to the patient’s scalp while awake, giving
better surgical and anaesthetic access but slightly
less precision. Many surgical procedures including
tumour excision that utilised frames in the past are
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Neurosurgery

now excised reliably with image guided technology
such as Brain Lab®.

ANAESTHESIA FOR

NEUROMODULATION

PREOPERATIVE MANAGEMENT

Stimulators that are inserted for neuromodulation
include occipital nerve stimulators (ONSs), sacral
nerve stimulators and spinal cord stimulators.

If undertaking awake testing, drugs that inhibit
tremor or rigidity in Parkinson and movement dis­
orders may need to be withdrawn as they will mask
the symptoms being assessed during surgery.

PERIOPERATIVE MANAGEMENT
• Procedures can be prolonged; pay attention to
positioning; insert a urinary catheter.
• When attaching the frame a short-acting
opiate should be given as this is particularly
stimulating.
• Once the frame is in place, access to the airway
is challenging. Alternative airway management
devices such as LM and a fibre-optic scope
should be accessible as well as the key to
dismantle the frame.
• An awake technique is preferable in those in
which somatotrophic localisation is required,
e.g. thalamotomy or pallidotomy, DBS insertion
and some epilepsy surgery.
• Several sedation techniques have been
described including the use of midazolam,

remifentanil and propofol. All should be used
with caution to avoid airway compromise;
capnography is advisable.
• For general anaesthesia, follow the same
principals for all neurosurgical cases.
• TIVA may be preferable as this will mean
continuous anaesthesia while transferring
patients to scanners.

POSTOPERATIVE MANAGEMENT
• Stereotatic surgery has lower morbidity and
mortality compared with more invasive
procedures.
• Following 2–4 hours in recovery patients can
return to a neurosurgical ward.
• Complications include broken or misplaced
leads, infection, seizures, intracranial
haemorrhage and air embolism.
360

OCCIPITAL NERVE STIMULATORS
A greater occipital nerve stimulator is a treatment
recommended by NICE for chronic migraine when
medical management has failed. The procedure is
usually done in 2 stages:
1.Under local anaesthesia and fluoroscopic

guidance, the electrodes are tunnelled under
the skin and placed over the occipital nerves.
Placement is confirmed by stimulation and

patient feedback. A lead is then tunnelled to
an exit site where it is connected to an external
stimulator.
2.If stage 1 is successful, the neurostimulator is
surgically inserted in the infraclavicular region
or abdominal wall under general anaesthetic.
The patient operates the stimulator by remote
control.
Anaesthetic management
The anaesthetic management is straightforward.
Patients should be counselled that the trial should
be done under local anaesthesia to allow for awake
testing. When implanting the stimulator, a general
anaesthetic using a laryngeal mask is acceptable
although if implanting in the abdomen muscle relaxants may be required.

SPINAL CORD STIMULATORS
Spinal cord stimulators are recommended by NICE
as a treatment for chronic neuropathic pain in
patients that have suffered pain for over 6 months
despite medical management and have had a successful trial. During the initial trial the leads are
passed percutaneously using a Tuohy needle into
the epidural space and then attached to a temporary external stimulator. If the patient can tolerate
the stimulation and pain scores are improved, then


Anaesthesia for non-craniotomy neurosurgery

they are suitable for implantation. The electrodes can
then be put in place either percutaneously or surgically and the neurostimulator implanted either in the

buttock area or abdomen.
Anaesthetic management
• Chronic pain medication should be continued
perioperatively.
• Patient’s need to be positioned prone and as
such need to be intubated and ventilated.
• Postoperatively patients are likely to require
long-acting opioid analgesia due to the
increased analgesic requirements often seen in
chronic pain patients.

SACRAL NERVE STIMULATORS
Sacral nerve stimulation was initially developed for
patients with urinary retention but is now employed
to treat faecal incontinence, constipation and chronic
pelvic pain. Sacral nerve stimulators can be inserted
under local or general anaesthesia. During the initial trial, an incision is made over the lower back and
the electrodes placed in contact with the sacral nerve
roots. These are then connected to an external stimulator for a period of about 2–3 weeks. If successful,
the leads are then tunneled beneath the skin to the
buttock or lower abdomen, where the pulse generator is sited.
Anaesthetic management
• If using a general anaesthetic technique, for
placement of the electrodes muscle relaxants
must be avoided as correct electrode placement
is identified using perineal and foot movement
to stimulation.
• Patients are positioned prone and appropriate
care must be paid to pressure points.
• This procedure carries a high degree of

postoperative discomfort. Opioids, in addition
to simple analgesic therapies, will be required.

ANAESTHESIA FOR PROCEDURES
TO RELIEVE HYDROCEPHALUS
Hydrocephalus has a variety of causes, which largely
fall into two groups:

• Obstruction of CSF outflow (noncommunicating hydrocephalus)
• Space-occupying lesion
• SAH
• Spina bifida
• Arnold–Chiari malformation
• Head injury
• Failure of absorption of CSF by the arachnoid
villi (communicating hydrocephalus)
• SAH
• Meningitis
• Head injury
In acute and emergency scenarios, surgeons will
opt to insert an external ventricular drain (EVD).
These are usually inserted into the frontal horn of
the lateral ventricle. The drain reduces the ICP and
provides a means to measure ICP but is only appropriate for short-term management given the risk of
infection. If patients are likely to suffer from hydrocephalus long term or if they have a more insidious
presentation, a shunt is inserted. Shunts permit the
drainage of CSF to distal sites including peritoneum,
atrium and pleura.

ANAESTHETIC MANAGEMENT

Preoperative
• Emergency patients will often be intubated and
ventilated in ICU or arrive as an emergency
transfer from a non-neuroscience centre.
• Patients should be assessed for signs of raised
ICP, including headache, vomiting and altered
level of consciousness.
• Vomiting can lead to dehydration and
electrolyte disturbance.
• Shunt procedures are more common in
children who need to be assessed for
prematurity and congenital abnormalities.
• Blocked shunts can present as acute cases when
patients may have a full stomach or decreased
conscious level.
Perioperative
• Routine anaesthetic monitoring should be
instituted in the emergency situation and a
rapid sequence induction may be required.
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Neurosurgery

• Patients with SAH or meningitis may have
intra-arterial monitoring in place but it is not
necessary for all EVD insertions.
• Patients are typically placed in the supine
position, although the lateral position is
required for a lumboperitoneal shunt. The

head may be held in the three-point pin
system to facilitate some shunt and endoscopic
procedures.
• Patients may require bolus doses of opioids to
cover the period of subcutaneous tunneling
during shunt surgery as it is highly stimulating.
Intraoperative complications
• Hypotension can occur following the release
of CSF and reduction in ICP; bradycardias may
also occur.
• Subcutaneous tunneling of the distal portion
of the shunt may cause pneumothorax or
haemothorax, and there is a significant risk of air
embolus during ventriculoatrial shunt creation.
Postoperative management
• If appropriate, patients should be woken
with minimal coughing and straining. Some
emergency cases should be kept intubated and
ventilated although the reduction in ICP may
improve their GCS significantly higher than
their preintubation level.
• Analgesia should include regular paracetamol
and non-steroidal anti-inflammatory drugs
(NSAIDs). Morphine may be required for the
initial 24 hours.
• Any new focal neurological signs should
prompt an urgent CT scan in order to rule out
intracranial haematoma.

REFERENCES

National Institute for Health and Care Excellence.
(2013). Occipital nerve stimulation for intractable
chronic migraine. IPG452. April.
National Institute for Health and Care Excellence.
(2008). Spinal cord stimulation for chronic pain
of neuropathic or ischaemic origin. TA159.
October.
362

National Institute for Health and Care Excellence.
(2004). Sacral nerve stimulation for faecal incontinence. IPG99. November.
Poon C, Irwin M. (2009). Anaesthesia for deep
brain stimulation and in patients with implanted
neurostimulator devices. Br J Anaesth 103:
152–165.
Suh JH, Vogelbaum MA, Barnett GH. (2004).
Update of stereotactic surgery for brain tumours.
Curr Opin Neurol 17: 681–686.

CROSS-REFERENCES
Complications of position, Chapter 30
Parkinson disease, Chapter 3
Epilepsy, Chapter 3

ANAESTHESIA FOR POSTERIOR
FOSSA SURGERY
ANATOMY
The posterior fossa houses the cerebellum, pons,
medulla, lower cranial nerves and fourth ventricle.
It is bounded by the tentorium above, the foramen

magnum below, the occiput posteriorly and the clivus anteriorly. Because of the restricted space, a
small degree of swelling in the posterior fossa can
have major neurological sequelae because:
• The pons and medulla contain the major
sensory and motor pathways, vital vascular
and respiratory centres and the lower
cranial nerve nuclei. Pressure on these
structures results in decreased conscious
level, hypertension, bradycardia, impairment
of protective airway reflexes, respiratory
depression and death.
• The pathway for CSF through the cerebral
aqueduct is very narrow and prone to
obstruction resulting in hydrocephalus.
Gross swelling will cause coning, either upwards
through the tentorium or downwards through the
foramen magnum. Because the respiratory centre
lies in the lower medulla, the latter leads to slow
irregular respiration progressing to apnoea.


Anaesthesia for posterior fossa surgery

PATHOLOGY
Tumours are the most common pathology in the
posterior fossa, particularly in children where they
account for 60% of all tumours. The pathologies that
require intervention are detailed in Box 14.3.

PREOPERATIVE MANAGEMENT

• Cranial nerve dysfunction may involve loss of
the gag reflex and patients may be suffering
from aspiration pneumonitis. If there is bulbar
involvement postoperative ventilation may be
required and/or a tracheostomy.
• Evaluation of cardiovascular status and the
ability to tolerate prone or sitting positions
must be carried out since hypertensive patients
will be prone to hypotension and cerebral
ischaemia. An echocardiogram should be
arranged for those undergoing surgery in the
sitting position. A patent foramen ovale (PFO)
is a relative contraindication to the sitting
position.
• Fluid and electrolyte status must be determined
since patients can be dehydrated and have
abnormal plasma electrolytes because of
vomiting or concurrent steroid therapy.

POSITIONING
Posterior fossa surgery can be done in supine, prone,
lateral, park bench or sitting positions.

PRONE
The prone position allows good surgical access to
midline structures, although bleeding may obscure
the surgical field. Careful padding of pressure points
and avoidance of increased venous pressure is
essential.

PARK BENCH
In the park bench position the patient is semiprone
with the head flexed facing the floor. It is used for lateral lesions, especially those in the cerebellopontine
(CP) angle. Careful padding is required to reduce

BOX 14.3:  Pathology
of posterior fossa lesions
▪▪ Tumours
– Axial: astrocytomas (most common in
children), medulloblastoma (most common
in adults), metastatic, brainstem glioma,
ependymoma, dermoid tumours and
haemangioblastoma
– Cerebellopontine angle: schwannoma,
meningioma, acoustic neuroma, glomus
jugulare tumour
▪▪ Vascular lesions
– Angiomas, arteriovenous malformations and
aneurysms (all uncommon)
– Nerve decompression for hemifacial spasm
and trigeminal pain
– Haematomas: spontaneous and traumatic

the risk of pressure damage to peripheral nerves and
excessive flexion/rotation of the neck must also be
avoided.

SITTING
The sitting position carries the highest risk and
should only be used by experienced clinicians in

carefully selected cases. Advantages include good
surgical access to midline tumours and decreased
blood loss. However, there are substantial risks,
including cardiovascular instability, decreased cerebral perfusion, air embolism, airway obstruction and
pneumoencephalus. The sitting position is achieved
by removing the head end from a standard operating table, placing the middle portion in the vertical position and arranging the patient’s legs in a
flexed position to ensure the buttocks remain firmly
wedged against the vertical part of the table. The
head is held in a three- point pin fixator mounted on
a frame across the table. Excessive head flexion must
be avoided to prevent jugular compression, swelling
of the tongue, and facial and cervical cord ischaemia.
A gap should be maintained between the chin and
suprasternal notch and care taken to avoid pressure
damage to peripheral nerves.
363


Neurosurgery

AIR EMBOLISM
Venous air embolism (VAE) can occur whenever
the operative site is above the level of the heart,
particularly if large areas of tissue are exposed. Air
may enter via dural vessels, dural sinuses, or vessels within a lesion. The greater the head-up tilt, the
greater the negative hydrostatic pressure between
open veins and the heart, and the greater the rate at
which air can be entrained. VAE is particularly common in the sitting position when an 8%–25% incidence is reported.

PATHOPHYSIOLOGY

Morbidity and mortality are directly related to the
rate and volume of entrained air. Although the fatal
dose of air embolus is unknown, it is likely to be of
the order of 100–300 mL. Air is drawn through the
right atrium and ventricle into the pulmonary arterioles. Although large volumes (>3 mL kg–1) act as an
airlock and cause circulatory failure, microvascular
bubbles result in activation and release of endothelial mediators, leading to an increase in pulmonary
vascular resistance, a fall in left atrial and ventricular
filling and a consequent reduction in cardiac output. Ventricular ectopic beats are common and gas
exchange is impaired as physiological dead space
increases, causing ventilation–perfusion (V/Q) mismatch, an acute reduction in ETCO2, increase in
PaCO2 and a reduction in PaO2.

DETECTION
Precordial Doppler, end-tidal nitrogen, pulmonary
artery catheters and transoesophageal echocardiography have all been used to detect VAE. Capnography
is generally regarded as the most useful monitor for
VAE, with a fall in ETCO2 being an indication for
immediate intervention.

PREVENTION

364

Volume loading reduces the fall in CVP as the patient
is tilted head-up. CVP must be monitored in all
cases and the tip of the catheter should be correctly
placed. The use of positive end-expiratory pressure
is controversial because, although it increases right

atrial pressure and might minimize air entrainment, it may adversely affect surgical conditions and
increases the risk of paradoxical air embolus if VAE
does occur. Compression of the lower limbs and/
or abdomen, by the use of leg bandages, a G-suit
or medical anti-shock trousers, raises venous pressure. Nitrous oxide should not be used as it will
cause expansion of any air bubbles that enter the
circulation.

MANAGEMENT
The aims of management are to stop further air
entry, remove air already present and treat cardio­
respiratory collapse. Immediate measures include:
• Notifying the surgeons and instructing them to
flood the operative area with saline and cover
the wound with wet swabs.
• Giving 100% oxygen.
• Raising venous pressure by levelling the table
and compressing neck veins.
• Aspirating via the CVP line; as well as guiding
therapeutic increases in venous pressure and
reductions in the hydrostatic gradient, CVP
catheters can also be used to aspirate air that
has entered the circulation; for optimum
recovery of air, the tip of the catheter should be
close to where the superior vena cava enters the
right atrium.

PARADOXICAL AIR EMBOLISM
Postmortem studies show that approximately 25% of
the population has a patent foramen ovale, a potential route for air to pass from the right to left atrium.

Whereas the presence of small amounts of air in the
venous circulation and pulmonary vascular bed may
not adversely affect the patient, the presence of minimal volumes (100–150 μL kg–1) in the arterial circulation can be fatal since a small air embolism reaching
the cerebral or coronary circulation will result in
irreversible damage. In addition, if air enters the
pulmonary circulation, the resultant obstruction to
flow will cause the pressure to rise on the right side
of the heart and fall on the left, thereby increasing
the pressure gradient and potentially reversing flow
through the shunt. Other anatomical routes, such as


References

arteriovenous shunts, may also allow air to pass from
the right to the left side of the circulation.

OTHER INTRAOPERATIVE
CONSIDERATIONS
• Although the choice of anaesthetic agents is not
critical, nitrous oxide should not be used.
• Routine monitoring should be used with the
addition of invasive blood pressure monitoring
to allow for accurate control of blood pressure.
• Central venous catheters are frequently used
particularly when using the sitting position as
this allows measurement of venous pressure
and may assist in the aspiration of a VAE.
• Damage to midbrain vital centres and cranial
nerves through direct intervention, retraction

or occlusion of blood supply may result in
sudden changes to systemic physiological
variables.
• Dramatic and abrupt cardiovascular changes
may also occur and the surgeon should be
advised of any significant instability. Drugs
such as atropine and beta-blockers should
be avoided if possible since they will mask
midbrain responses to surgical manipulation.
• Electrophysiological techniques, such as
somatosensory-evoked potentials, are
increasingly used to monitor the integrity of
crucial pathways during complex posterior
fossa surgery.
• The facial nerve (VII) is stretched across the
capsule of acoustic neuromas and monitoring
of the VIIth nerve function is often performed
to minimize the risk of intraoperative damage.
During VIIth nerve monitoring, neuromuscular
blocking agents should be avoided after the
initial dose used for intubation.
• Normotension should be achieved prior to
surgical closure to confirm the adequacy of
haemostasis.

POSTOPERATIVE MANAGEMENT
• Following posterior fossa surgery, patients
should be managed in a critical care
environment.

• Patients who were neurologically intact
preoperatively and had uneventful surgery should
be extubated, avoiding coughing and straining
and monitored in a high dependency area.
• Poor preoperative neurological status, adverse
intraoperative events, prolonged surgery
with significant tissue retraction and a lesion
>30 mm in diameter with mass effect are
all indicators of possible slow recovery from
anaesthesia and the potential need for elective
postoperative ventilation.
• Postoperative swelling in the posterior fossa
is a potentially life-threatening complication.
The small anatomical space, tendency of
the cerebellum to swell following prolonged
retraction and the risk of bleeding all add to the
threat. A reduced respiratory drive may result
from, and in its turn increase, swelling. This
may be delayed, sometimes developing hours
after an initially good recovery. Deterioration in
neurological status after posterior fossa surgery is
therefore an indication for an immediate CT scan.
• Hydrocephalus may occur as a result of
occlusion of CSF outflow and insertion of an
EVD may be necessary.
• Macroglossia is a rare but potentially lifethreatening complication. It is likely to be
related to occlusion of lingual drainage during
prolonged surgery with excessive neck flexion,
and may also be associated with the use of an
oropharyngeal airway intraoperatively.

• The gag reflex may be obtunded as a result of
swelling or damage to the glossopharyngeal
and vagus nerves. A nasogastric tube and nilby-mouth orders are indicated after surgery for
large lesions and should be continued until the
gag has been formally assessed postoperatively.
• Postoperative nausea and vomiting is common,
especially following CP angle surgery.
Multimodal antiemetic therapy is often
required.

REFERENCES
Gale T, Leslie K. (2004). Anesthesia for neurosurgery in the sitting position. J Clin Neurosci 11:
693–696.

365


Neurosurgery

Harrison E, Mackersie A, McEwan A, Facer E.
(2002). The sitting position for neurosurgery in
children: A review of 16 year’s experience. Br J
Anaesth 88: 12–17.
Jagannathan S, Krovvidi H. (2014). Anaesthetic
considerations for posterior fossa surgery. Contin
Educ Anaesth Crit Care Pain 14: 202–206.
Joshi S, Dash HH, Ornstein E. (1997). Anesthetic
considerations for posterior fossa surgery. Curr
Opin Anaesthesiol 10: 321–326.
Pandia M, Bithal P, Sharma M et al. (2009). Use of

spontaneous ventilation to monitor the effects
of posterior fossa surgery in the sitting position.
J Clin Neurosci 16: 968–969.
Rath G, Bithal P, Chaturvedi A, Dash H. (2007).
Complications related to positioning in posterior
fossa craniectomy. J Clin Neurosci 14: 520–525.
Smith D. (2010). Anesthetic management for posterior fossa surgery. In: Cottrell J, Young W (Eds.).
Cottrell and Young’s Neuroanesthesia. Philadelphia:
Mosby Elsevier.
Smith M, Hunt K. (2009). Neurosurgery. In: Allman
K (Ed.). Emergencies in Anaesthesia, 2nd edn.
Oxford: Oxford University Press.

CROSS-REFERENCES
Complications of position, Chapter 30
Raised ICP, Chapter 30

ANAESTHESIA FOR SPINE
SURGERY
The scope of spinal surgery is vast. Patients usually
present with one of five pathologies at any site from
cervical to lumbosacral:
•
•
•
•
•

366

Trauma (unstable vertebral fractures)
Infection (epidural abscess)
Malignancy (either primary or metastatic)
Congenital (scoliosis)
Degenerative

In an ageing population with a growing lower
back pain problem, the majority of spinal cases are
simple laminectomies and microdiscectomies but
many cases involve high-risk multiple level surgery

with major blood loss. All present significant challenges to the anaesthetist.

SURGICAL APPROACH
The majority of spinal procedures are performed in
the prone position with a few notable exceptions
(anterior cervical surgery, thoracic discectomies).
There are multiple complications to proning patients
detailed in Box 14.4. However, if the right precautions and equipment are used the complications will
be minimised.
Pillows, gel pads and foam bolsters can be constructed to support the patient ensuring:
• The abdomen is free.
• The head is at or above the level of the heart
in a neutral position using a head rest or a
Mayfield head fixator.
• The eyes are taped closed, without padding and
free from external pressure, regularly checking
them where possible.
• The arms are in a natural position no more
than 90° abduction with slight internal rotation

paying particular attention to the ulnar nerve at
the elbow.
Specific devices are available to facilitate proning:
Montreal mattress, Jackson operating table, Wilson
Frame and the Andrews operating table. A commonly used alternative to the classic prone position
is the knee-elbow position whereby the patient has
a foam bolster under their chest, their elbows and

BOX 14.4: Complications
of the prone position
▪▪ Accidental extubation
▪▪ Ophthalmic complications (corneal abrasions,
postoperative visual loss)
▪▪ Peripheral nerve injury (ulnar nerve at elbow,
brachial plexus)
▪▪ Pressure injuries (skin necrosis, breast/genital
injury)
▪▪ Abdominal compression (venous congestion
in epidural veins, organ ischaemia, impaired
ventilation and reduced cardiac output)


Anaesthesia for spine surgery

arms lie beneath them on the operating table and
their bottom rests on a support. This has the advantage of keeping the abdomen free and can reduce the
lumbar lordosis and improve surgical access for lumbar surgery but can be technically difficult to do if
the personnel positioning are not experienced with
the position.

on the exposed spinal cord at surgery. SSEPs and
MEPs are sensitive to anaesthetic agents. SSEPs are
preserved with low/modest dose volatile agent and
during intravenous anaesthesia. MEPs are more sensitive and intravenous anaesthesia techniques, with
a high-dose remifentanil and no muscle relaxant,
are required.

INTRAOPERATIVE
CONSIDERATIONS

AIRWAY MANAGEMENT

MONITORING
For simple, single-level spinal procedures routine
monitoring, including ECG, noninvasive blood pressure monitoring, pulse oximetry, capnography and
temperature are adequate. Arterial blood pressure
monitoring is required for complex or prolonged procedures when substantial blood loss is anticipated,
serial blood gas monitoring is required, there are
concerns about spinal cord perfusion or in the presence of significant comorbidities. A central venous
catheter (CVC) can assist with fluid balance management or delivery of inotropes/vasopressors. The
internal jugular or subclavian routes may be used
for thoracic or lumbar procedures, whereas a femoral
CVC is more frequently used for cervical approaches.
A urinary catheter is mandatory for long procedures
and when significant blood loss is anticipated.

EVOKED POTENTIAL MONITORING
Evoked potentials are used during spinal surgery
to identify potentially reversible changes in spinal
cord function and allow intervention before permanent neurological damage occurs. Somatosensoryevoked potentials (SSEPs) monitor the integrity

of the sensory pathway, specifically the dorsal column. SSEPs are recorded from the cerebral cortex
using scalp electrodes following electrical stimulation of a peripheral nerve. Motor-evoked potentials
(MEPs) allow the integrity of the motor pathways to
be assessed. MEP monitoring involves transcranial
stimulation (electrical or magnetic) of the motor cortex with the evoked responses being recorded most
commonly as compound motor action potentials in
peripheral muscles, but occasionally via epidural/
intrathecal electrodes or an electrode placed directly

Difficult laryngoscopy is common in patients with
disease of the upper three cervical vertebrae and airway access with an alternative to direct laryngoscopy
may be required. Patients with limited extension at
the craniocervical junction tend to also have poor
mouth opening because of a direct effect as well as an
association with temporomandibular joint disease.
There is no evidence that any method of airway
management has a better outcome than another in
patients with an ‘unstable’ cervical spine. External
cervical spine fixation devices make direct laryngoscopy more difficult and an alternative technique
(e.g.  awake fibre-optic intubation) rather than the
application of force should be used.

BLOOD LOSS
Massive blood loss can occur during spinal surgery
particularly in scoliosis surgery and extensive stabilisations. In the prone position, venous return via the
IVC can be obstructed and blood then travels back
to the heart via epidural veins leading to the risk of
large blood loss from these veins. Although venous
bleeding is usually insidious, it can be responsible
for major blood loss. Catastrophic bleeding can occur

as a result of injury to major vessels, including vertebral or carotid injury during cervical surgery, iliac
artery injury during abdominal approaches and penetration of the aorta by misplaced pedicle screws or
rongeurs during lumbar microdiscectomy. Adequate
large-bore venous access, rapid transfusors, cell salvage and readily available blood and blood products
should be available for all major spinal cases.

TEMPERATURE
Exposure of patients during prolonged induction of anaesthesia (e.g. during awake fibre-optic

367


Neurosurgery

intubation), patient positioning and X-raying can
lead to pronounced hypothermia prior to the start of
surgery. Patients should be kept warm with forced
warm air blankets and heated fluids since hypothermia can contribute to morbidity in terms of coagulopathy and increased infection rates.

ANALGESIA
Spinal procedures are frequently painful. In addition to pre-existing neuropathic pain, extensive
muscle retraction and disruption can lead to muscle
injury and ischaemia, resulting in severe postoperative pain. With straightforward discectomies
paracetamol, a long-acting opiate and local anaesthetic to the wound may be sufficient. If the patient
is on extensive chronic pain medication, all pain
medications should be continued perioperatively,
gabapentin or pregabalin should be considered preoperatively if not already taken and additional analgesic such as ketamine or clonidine may be required
intraoperatively. Major spinal surgery pain can be
severe. Additional acute pain techniques including
ketamine, clonidine and local anaesthetic infusions

are utilized intraoperatively and postoperatively on
critical care units in some centres.

INTRAOPERATIVE NEUROLOGICAL
DETERIORATION

368

Spinal cord injury (SCI) can occur during anaesthesia in patients with normal spines and is usually
related to poor positioning or severe hypotension.
Spinal abnormalities, including spinal stenosis,
instability or pre-existing myelopathy, increase the
risk of intraoperative SCI.
Reports of cervical SCI during anaesthesia are
often raised by non-anaesthetists and may confuse
association with causation. The proposed mechanism is acute cord compression during airway
management, but studies of cervical movement during intubation in unstable spinal preparations do
not support this concept. The injuries described in
the reports (usually central and anterior cord syndromes) would be better explained by hypoperfusion
and it is likely that most of these injuries are due to
a combination of hypoperfusion and malposition for
extended periods of time.

POSTOPERATIVE CONSIDERATIONS
• An appropriate postoperative destination
must be chosen to facilitate pain control,
haemodynamic monitoring or postoperative
ventilation.
• Airway obstruction – There is a small incidence
of airway obstruction after anterior cervical

surgery. This can be due to a postoperative
haematoma or, more likely, marked tissue
swelling of the pharynx or upper airway.
Patients may complain of ‘not being able
to breathe’ and want to sit up. They rarely
have stridor and do not desaturate until the
obstruction is nearly complete. Opening the
wound is a priority even if a haematoma is
not suspected, since this reduces lymphatic
and venous obstruction and improves
airway patency. Following evacuation of the
haematoma or relief of tissue pressure, a
tracheal tube should be left in situ for at least
24 hours until swelling subsides.
• Postoperative neurological deterioration –
Meticulous neurological observation is required
to elicit any signs of spinal haematoma
formation.
• Venous thromboembolism (VTE) – Spinal surgery
patients are at high risk of postoperative VTE
because of prolonged surgery, paresis, tumour
resection and postoperative immobility.
Graduated compression stockings and
intermittent calf compression should be used in
all patents and low-molecular-weight heparin
instituted after 12–24 hours.
• Aperients – Large opioid requirements and
immobility make constipation a frequent
postoperative problem.
• Early mobilization – In conjunction with

physiotherapy, early mobilization reduces
postoperative respiratory tract infections
and VTE.

REFERENCES
Feix B, Sturgess J. (2014). Anaesthesia in the prone
position. Contin Educ Anaesth Crit Care Pain 14:
291–297.


Anaesthesia for supratentorial surgery

Haldeman S, Kohlbeck FJ, McGregor M. (2002).
Unpredictability of cerebrovascular ischemia
associated with cervical spine manipulation
therapy: A review of sixty-four cases after cervical spine manipulation. Spine 27: 49–55.
Harrop JS, Sharan AD, Vaccaro AR, Przybylski GJ.
(2001). The cause of neurologic deterioration after
cervical spinal cord injury. Spine 26: 340–346.
Nowicki R. (2014). Anaesthesia for major spinal
surgery. Contin Educ Anaesth Crit Care Pain 14:
147–152.
Prielipp RC, Warner MA. (2009). Peripheral nerve
injury: A silent scream. Anesthesiology 111: 490–497.
Raw DA, Beattie J, Hunter J. (2003). Anaesthesia for
spinal surgery in adults. Br J Anaesth 91: 886–904.
Sagi HC, Beutler W, Carroll E, Connolly PJ. (2002).
Airway complications associated with surgery on
the anterior cervical spine. Spine 27: 949–953.

ANAESTHESIA FOR
SUPRATENTORIAL SURGERY
Anaesthesia for supratentorial surgery is indicated
for a wide range of pathologies. The anaesthetist’s
knowledge and skill to manipulate the intracranial
physiology is vital to optimise surgical conditions
and improve the outcome of the patient.

ANATOMY AND PATHOLOGY
The supratentorial region of the brain consists predominantly of the cerebral hemispheres and their
meninges. Indications for surgery are detailed in
Box 14.5 and the aetiologies are in Box 14.6. Tumours
make up the vast majority of elective surgery. It is
BOX 14.5:  Indications
for supratentorial surgery
▪▪ Burrhole biopsy for histological diagnosis of a
lesion
▪▪ Craniotomy for excision or debulking of tumour
▪▪ Aspiration of cerebral abscess for antibiotic
resistance
▪▪ Vascular procedures
▪▪ Evacuation of haematomas

BOX 14.6: Aetiology of brain
tumours in adults
▪▪
▪▪
▪▪
▪▪
▪▪

▪▪
▪▪

Glioma
Meningioma
Metstasis
Schwannomas
Pituitary adenomas
Medulloblastomas
Craniopharyngiomas

BOX 14.7: Presenting
symptoms of brain tumours
▪▪
▪▪
▪▪
▪▪
▪▪
▪▪
▪▪
▪▪

Headache
Nausea and vomiting
Seizures
Visual disturbances
Focal neurology
Speech difficulties
Confusion and behavioural changes
Hearing problems

the most common site for brain tumours in adults but
only one-third in children. The usual presentation is
described in Box 14.7.

PREOPERATIVE MANAGEMENT
• In addition to the diagnostic CT head, further
CT or MRI imaging may be required to aid an
image-guided technique or a digital subtraction
angiography to determine how vascular the
lesion is.
• The neurological status of the patient should
be carefully documented so any postoperative
deterioration can be identified.
• All routine medication excluding
anticoagulants should be continued
perioperatively, particularly corticosteroids and
anticonvulsants.
• Clotting studies and blood cross-match should
be arranged particularly for the meningiomas
and vascular tumours.
• Blood glucose and urea and electrolytes may flag
up hyperglycaemia secondary to steroid use and
sodium abnormalities related to the tumour.

369


Neurosurgery

• Sedative premedications should be given with
caution and if given the patient should be
monitored.

INDUCTION
• As per the basic principals of neuroanaesthesia,
the induction should be smooth avoiding
coughing, straining, swings in blood pressure
and ICP. This is usually undertaken with
propofol and a short acting opiate like fentanyl
or remifentanil.
• Orotracheal intubation should be facilitated
with a nondepolarising muscle relaxant and
then fixed securely with adhesive tape, avoiding
ties to prevent obstruction of cerebral venous
drainage.
• Standard monitoring and temperature should
be included with all patients and many cases
require direct blood pressure monitoring.
Central venous access should be considered in
particularly long cases where multiple infusions
are being used.
• Urinary catheters should be inserted for all long
operations and those likely to involve the use of
osmotic therapy.
• If the surgeons are using image-guided
surgery, they may ask you to delay applying
waterproof dressing to the eyes, so as not to
interfere with navigation.

POSITIONING
The position is dictated by the surgical approach,
although the supine position is satisfactory for many
cases.
• Head-up tilt (10°–15°).
• Avoid excessive head rotation or flexion since
this impairs cerebral venous drainage.
• Secure the head with a horseshoe headrest or
three-point pin fixator (bolus dose of opioid to
prevent hypertension during pinning).
• Before draping check that there are no loose
connections/kinks in the breathing circuit and
that there is unimpeded access to intravenous
cannulae.
370

MAINTENANCE
There are some theoretical advantages but no proven
outcome benefits to the use of TIVA in neurosurgery.
However, unless the ICP is critically raised, many
anaesthetists use a balanced technique with controlled ventilation, short-acting opioids and a volatile
agent such as sevoflurane or desflurane.
• Adjust ventilation to maintain PaCO2 between
4.5 and 5.0 kPa.
• Air–oxygen mix with FiO2 0.3–0.5.
• Avoid nitrous oxide.
• Volatile agents should be used at doses below
1.0 MAC to avoid increases in cerebral blood flow.
• Remifentanil infusion allows easy control of
cardiovascular variables during periods of

surgical stimulation and rapid emergence.
• Normothermia should be maintained using
a warming mattress, warm air blanket and
warmed fluids.
• A balanced salt solution should be used as
maintenance fluid, but bear in mind that
large volumes of normal saline can produce
hyperchloraemic metabolic acidosis. Blood loss
should be replaced with packed red cells and
glucose-containing solutions avoided.
• Steroids such as dexamethasone can be given
perioperatively to reduce cerebral oedema and
prevent postoperative nausea and vomiting.
• All patients should receive prophylactic
antibiotics according to local guidelines.
• Deep vein thrombosis (DVT) prophylaxis
should include the use of graduated
compression stockings and pneumatic calf
compression.

INTRAOPERATIVE MANAGEMENT
OF A TIGHT BRAIN
Bulging dura on removal of the craniotomy flap
indicates a ‘tight’ brain and the following manoeuvres can be used to prevent cerebral ischaemia and
improve operating conditions:
• Check head position and use reverse
Trendelenburg.


Anaesthesia for supratentorial surgery

• Ensure CO2 is 4.5–5.0 KPa. If necessary
temporary hypocapnia 4.0–4.5 KPa can be
considered if all other treatments have failed.
• Control blood pressure, particularly in a nonautoregulating brain.
• Dexamethasone 4–10 mg if not already given.
• Switch to TIVA if using volatile.
• Osmotic therapy: mannitol 0.25–1 g/Kg,
hypertonic saline 3%–7.2% 30–150 mL/h or
furosemide 10–20 mg boluses.

BOX 14.8:  Postoperative
complications
▪▪
▪▪
▪▪
▪▪
▪▪
▪▪
▪▪

Bleeding at the operative site
Subdural haematoma
Pneumocephalus
Seizures
Cerebrospinal fluid leak
Infarct
Infection

EMERGENCE

• Prior to closure, return the blood pressure to
normal while the surgeon ensures haemostasis.
• As with induction, the emergence and extubation
should be smooth and avoid straining, coughing,
swings in ICP and blood pressure. There are
various techniques used to achieve this including
extubating deep and inserting a laryngeal mask
but more frequently anaesthetists will extubate
while the patients are on a remifentanil infusion
as an antitussive agent.
• Give analgesia (morphine) and antiemetics
(ondansetron, cyclizine).
• Treat emergence hypertension with an
antihypertensive (labetolol).
• Consider postoperative ventilation only if the
patient was severely obtunded preoperatively or
there have been intraoperative problems.
• ICP should be monitored if the patient will be
sedated and ventilated in the postoperative
period.

POSTOPERATIVE MANAGEMENT
• Most postoperative complications occur in the
first 6 hours; Box 14.8.
• After supratentorial surgery patients experience
moderate to severe pain and analgesia should
include regular paracetamol and opioids either
orally or via PCA.
• For patients with known pain problems, a scalp
block should be considered.

• Postoperative nausea and vomiting are
common and antiemetics should be prescribed
prophylactically.

• Mechanical methods of DVT prophylaxis
should be continued until the patient is
mobilizing. Low-molecular-weight heparin is
used in consultation with the neurosurgeon but
is probably safe after 24 hours.

AWAKE CRANIOTOMY
This is the technique of choice for surgical procedures in which lesions are adjacent to or within
eloquent areas in the motor and sensory strip, and
speech area. It can also be used during epilepsy
surgery when intraoperative electrocorticography
(ECoG) is being used to define the resection margins
precisely and during deep brain surgery to facilitate
accurate placement of stimulating electrodes. Awake
craniotomy allows the patient’s neurological status
to be assessed continually during surgery so that
maximal resection can be achieved while minimizing the risk of permanent damage. The technique is
growing in popularity due to the increased survival,
reduced length of stay and postoperative complications. It should now be considered for all supratentorial tumours not just those in eloquent areas.

PREOPERATIVE
PREOPERATIVE ASSESSMENT
The key to successful awake surgery is the relationship between patient, surgeon and anaesthetist.
• Identify those patients in whom
contraindications (Box 14.9) to awake surgery
exist.

371


Neurosurgery

BOX 14.9: Contraindications
to awake craniotomy
▪▪ Absolute
– Patient refusal
– Inability to stay still
– Inability to cooperate (confusion)
▪▪ Relative
– Gross obesity
– Difficult airway
– Anxiety
– Extreme response to pain
– Communication problems
– Obstructive sleep apnoea
– Young age
– Poor motivation

• The anaesthetist should explain all of the
steps of the proposed technique in detail,
highlighting that the aim is to provide an
awake, lucid and pain-free experience during
intraoperative testing.
• Patients may be seen by neuropsychologists if
the lesion involves speech and language areas
and they determine what neurological function
is going to be tested and document baseline

responses.
• Explain to patients that they should
communicate with the anaesthetist if they feel
pain, anxiety or nausea and reassure them that
these problems can be dealt with quickly and
effectively.

INTRAOPERATIVE
Many combinations of sedation, analgesia and
anaesthetic techniques have been described, each
with their advocates and proposed advantages.
Essentially there are three parts to the operation:
• Craniotomy
• Tumour excision
• Closure
The key principal of an awake craniotomy is that
the patient is either awake or lightly sedated during the tumour excision. The patient can be asleep
for the craniotomy preparation stage and the closure;
372

this is known as the asleep, awake, asleep technique
where usually a laryngeal mask airway is used to
maintain the airway. The choice of technique will be
determined by the surgeon, pathology, length of surgery and patient factors. The essential anaesthesia
requirements are
• Optimal analgesia during painful stimuli
• Prevention of nausea, vomiting and seizures
• Patient immobility and comfort during awake
testing and resection
• Whichever technique is chosen, effective local

anaesthesia is essential usually in the form of a
scalp block that can provide effective analgesia
for 8 hours

OTHER IMPORTANT INTRAOPERATIVE
CONSIDERATIONS
• Full anaesthetic monitoring, with most
anaesthetists inserting invasive blood pressure
monitoring and using capnography when the
patients are awake also.
• Urinary catheterization should be considered
for the longer operations. If not, then an adult
nappy could be offered should they need to
urinate intraop.
• BiS is particularly useful if using the asleepawake technique as it can minimize the amount
of propofol/volatile used and hence the patient
wakes up more promptly for functional testing.
• Clear surgical drapes should be used to reduce
feelings of claustrophobia during the awake
phase and positioned to allow continuous and
unimpeded access to the patient’s airway by the
anaesthetist.
• Antiemetics (ondansetron, cyclizine and
dexamethasone) should be given at the start of
surgery.
• Analgesia: paracetamol and a long-acting
opiate intravenously.
• Seizures can occur in up to 20% of cases,
usually during epilepsy surgery, and can be
treated with cortical irrigation with cold saline

or bolus doses of propofol. Magnesium up to
10 g given by slow intravenous infusion at the
start of surgery may also have some protective
effect.


References

• Loss of patient cooperation terminates any
possibility of useful functional testing and thus
imposes deepening of anaesthesia to ensure
the safe completion of surgery.
• Complications are summarized in Box 14.10.

AIRWAY MANAGEMENT
Whatever anaesthetic technique is chosen, there is
always the risk of airway/breathing problems and
strategies must be in place to deal with hypoventilation and airway obstruction. Difficult airway equipment and adjuncts should be available including
access to a fibre-optic scope.
Overall, awake craniotomy is a very safe procedure with minimal mortality and morbidity related
to the anaesthetic technique with several institutions
safely discharging patients home on the day.

REFERENCES
Burnand C, Sebastian J. (2014). Anaesthesia for
awake craniotomy. Contin Educ Anaesth Crit Care
Pain 14: 6–11.
Bhagat H, Dash H, Bithal P et al. (2008). Planning
for early emergence in neurosurgical patients: A
randomized, prospective trial of low-dose anesthetics. Anesth Analg 107: 1348–1355.

Cole C, Gottfried O, Gupta D, Couldwell W. (2007).
Total intravenous anesthesia: Advantages for

BOX 14.10:  Complications
of awake craniotomy
▪▪
▪▪
▪▪
▪▪
▪▪
▪▪
▪▪

Seizures
Nausea and vomiting
Dysphoric reaction
Respiratory depression
Airway obstruction
Air embolism
Loss of patient cooperation, leading to
conversion to general anaesthesia
▪▪ Brain swelling
▪▪ Focal neurological deficit

intracranial surgery. Neurosurgery 61(Suppl. 5):
369–377.
Dinsmore J. (2007). Anaesthesia for elective neurosurgery. Br J Anaesth 99: 68–74.
Li J, Gelb A, Flexman A, Ji F, Meng L. (2016).
Definition, evaluation, and management of
brain relaxation during craniotomy. Br J Anaesth

759–769.
Lobo F, Wagemakers M, Absalom A. (2016).
Anaesthesia for awake craniotomy. Br J Anaesth
116: 740–744.
Talke P, Caldwell JE, Brown R et al. (2002). A comparison of three anesthetic techniques in patients
undergoing craniotomy for supratentorial intracranial surgery. Anesth Analg 95: 430–435.

373





15

Thoracic surgery
MATTHEW STAGG

Bronchopleural fistula
375
References376
Anaesthesia for thoracic surgery –
general principles
376
References380
Inhaled foreign body
381
References382
Lobectomy382
References383

Mediastinal surgery
383

BRONCHOPLEURAL FISTULA
MATTHEW STAGG
Bronchopleural fistula (BPF) is a direct communication between the tracheobronchial tree and the
pleural cavity. Causes include dehiscence of bronchial stump, cancer, inflammatory lesions and
trauma. In developed countries, dehiscence of the
bronchial stump following pneumonectomy is the
most common cause. The incidence of BPF following pneumonectomy is extremely low in specialized
centres.
Minor forms of post-pneumonectomy BPF can be
sealed bronchoscopically with fibrin glue. Large fistulas require resuture of the bronchial stump via a
repeat thoracotomy.

References385
Pleurectomy and pleurodesis
386
References387
Pneumonectomy387
References388
Postoperative analgesia
388
References389
Rigid bronchoscopy
389
References390

PREOPERATIVE ASSESSMENT
AND INVESTIGATIONS

Symptoms relate either to accumulation of pneumothorax in spontaneously breathing patients, a difficulty providing IPPV due to significant leak or from
fluid from the infected space flowing over to the ‘normal’ lung.

SMALL BPF
• Malaise and low-grade fever
• Cough ± haemoptysis, wheeze or dyspnoea

LARGE BPF
• Severe dyspnoea and debilitation
• Coughing up copious amounts of thin brown
fluid

375


Thoracic surgery

INVESTIGATIONS
• Chest X-ray. Loss of pneumonectomy space
fluid. Consolidation/collapse of remaining lung.
• Blood gas analysis to assess hypoxaemia,
hypercarbia and acid-base status.

PREOPERATIVE PREPARATION
• General resuscitation including oxygen by
face-mask.
• Sit patient up to prevent further spillover.
• Insert chest drain on pneumonectomized side.
• Transport patient to theatre in sitting position
with drain open.

PREMEDICATION
• None required

MONITORING
•
•
•
•
•
•

376

Routine basic monitoring
Invasive arterial pressure
Central venous pressure
Arterial blood gases
Core temperature
Urine output

• Administer further muscle relaxant.
• IPPV via endobronchial portion of tube.
• Place patient in lateral position for thoracotomy.

POSTOPERATIVE MANAGEMENT
• Treat as for pneumonectomy.
• Sputum retention, infection, acute lung injury
(ALI) and respiratory failure are common and
carry a high mortality. Treat with physiotherapy,

antibiotics, ventilation and early tracheostomy.
• Infection in pneumonectomy space.

OUTCOME
• Mortality around 10%–20%

REFERENCES
Lauckner ME, Beggs I, Armstrong RF. (1983). The
radiological characteristics of bronchopleural
fistula following pneumonectomy. Anaesthesia
38: 452–6.
Ryder GH, Short DH, Zeitlin GL. (1965). The anaesthetic management of a bronchopleural fistula
with the Robertshaw double-lumen tube. Br J
Anaesth 37: 861–5.

ANAESTHETIC TECHNIQUE

CROSS-REFERENCES

Classically it has been advocated that a post-­
pneumonectomy fistula should be isolated with an
endobronchial tube before IPPV is employed. This can
be achieved either with awake endobronchial intubation with local analgesia of the airway (with or without
fibre-optic bronchoscopy) or inhalational induction
and intubation under deep inhalational anaesthesia.
These techniques should be discussed at examinations, but both are fraught with difficulty. Most experienced anaesthetists now use the following technique:

Bronchiectasis, Chapter 1
Bronchial carcinoma, Chapter 1
Pneumonectomy, Chapter 15

Postoperative analgesia for thoracic surgery patients,
Chapter 15
One-lung anaesthesia, Chapter 28
Preoperative assessment of pulmonary risk, Chapter 25

• Sit patient upright with drain open.
• Preoxygenate.
• Use intravenous induction and suxamethonium
or rocuronium.
• Perform rigid bronchoscopy.
• Insert double-lumen tube into the remaining
bronchus with fibre-optic bronchoscope.

ANAESTHESIA FOR THORACIC
SURGERY – GENERAL
PRINCIPLES
MATTHEW STAGG
Anaesthesia for thoracic surgery has evolved since
the 1930s when Gale and Waters (USA) and Magill


Anaesthesia for thoracic surgery – general principles

(UK) introduced single-lumen endobronchial tubes
for selective endobronchial intubation.
The majority of lung resections in the UK are carried out to treat lung cancer: 20% of patients with
lung cancer have resectable tumours. Thoracic surgery is very invasive and many patients are elderly
smokers with smoking associated comorbidities,
especially COPD and cardiac disease. The operative
mortality following pneumonectomy and lobectomy

is 6.2% and 2.4% respectively (Table 15.1). Increasing
numbers of procedures (including lobectomy) can be
undertaken thoracoscopically using video assisted
thoracic surgery (VATS).
Pulmonary resection is one of the most physiologically traumatic surgical procedures. The inflammatory and neurohumoral response is correspondingly
large. Inflammation is a trigger to arterial plaque
rupture and arterial thrombosis. Interleukin 6 (IL6)
plays a central role. Plaque rupture in the coronary
circulation may cause acute coronary syndrome
(ACS). An ACS, either unstable angina or MI (STEMI
or NSTEMI), is a major cause of death and morbidity.
The incidence of ACS is higher in thoracic surgery
than any other area except major vascular surgery.
Valvular heart disease is less common but relevant,
with the prevalence of significant aortic stenosis 3%
in those aged over 75. Cardiac failure has a prevalence of 2% in the sixth decade rising to 10% in the
eighth decade. Its presence carries a very high risk.
Rigid bronchoscopy and mediastinoscopy are
investigative procedures although bronchoscopy

can be used for therapeutic purposes. Pleurectomy is
used to treat recurrent spontaneous pneumothoraces
in young adults. All these are low risk. Pleurodesis is
undertaken for pneumothorax secondary to COPD
and for malignant pleural effusions. These patients
are usually debilitated and risk is higher (Table 15.1).
HDU care is always indicated following lung
resection or major mediastinal surgery. Most of the
complications of thoracic surgery are pulmonary or
cardiac. Some patients require postoperative ventilation as a result of the development of respiratory failure secondary to infection or acute lung injury (ALI).

The use of intravenous fluid during and following
lung resections should be cautious. Over-hydration
is associated with ALI and other pulmonary complications, especially after pneumonectomy.
Operations carried out through a posterolateral
thoracotomy are extremely painful. Poor analgesia
causes much distress and impairs both respiratory
function and sputum clearance; regional analgesia is
always advisable either in the form of paravertebral
blocks or thoracic epidurals. These have the benefit
of avoiding systemic opioids that may cause respiratory depression, atelectasis or cough suppression.

PREOPERATIVE ASSESSMENT
PULMONARY FUNCTION
• Clinical – check functional status, sputum
production and physical examination.

Table 15.1  Thoracic surgical results from 42 UK centres (2007–2008)
Lung resection for primary
malignant tumours
Pneumonectomy
Lobectomy
Segmentectomy/Wedge resection
Pleural procedures (open)
Pleurectomy/pleurodesis ± closure of air leak
VATS for pulmonary/pleural disease
Lobectomy
Wedge resection
Closure of air leak ± pleurectomy/
pleurodesis

Numbers

Deaths (%)

497
2800
508

31 (6.2)
68 (2.4)
7 (1.4)

379

9 (2.4)

146
161
1531

2 (1.4)
2 (1.2)
16 (1.0)

Source: Adapted from The database of the Society of Cardiothoracic Surgeons of
Great Britain and Ireland.

377